Turbine vanes are used for guiding the turbine's driving medium through the turbine so as to optimise momentum transfer from the driving medium to a rotor of the turbine. In gas turbines the driving mediums are hot and corrosive combustion gases. Therefore, the turbine vanes are usually coated with a thermal barrier coating system. However, in order to reduce gas turbine engines emissions and the specific power, one aims to achieve higher turbine entry temperatures of the combustion gas. This in turn means a higher thermal load on the turbine components, in particular on the turbine nozzle guide vanes, i.e. the first row of turbine vanes, which is facing the hot and corrosive combustion gas when it enters the turbine section of the gas turbine engine. The higher temperatures lead to increased corrosion of the nozzle guide vanes and, in particular, at the gas washed surfaces of the nozzle guide vanes' platforms.
To reduce the thermal load on the platform, the platforms are cooled by impingement cooling, i.e. by air jets directed onto their non gas washed surfaces. Such an impingement cooling is, e.g. disclosed in DE 10 2005 013 795 A1 or in WO 2007/000409 A1. Although impingement cooling has been sufficient with the current temperatures of the combustion gas entering the turbine section, it may be insufficient with future higher turbine entry temperatures of the combustion gas.
In EP 0 902 164 A1 is described another alternative for platform cooling. Thereby cooling fluid channels are located in the platform through a cooling fluid guide along the platform.